1. Field of the Invention
The present invention relates to a measuring apparatus and a measuring method for measuring a signal-under-test, a testing apparatus and a testing method for testing a device-under-test and an electronic device. More specifically, the invention relates to a measuring apparatus, a measuring method, a testing apparatus and a testing method for measuring jitters in the signal-under-test outputted out of the device-under-test.
2. Related Art
There has been known a test for measuring jitter in a signal-under-test outputted out of an electronic device such as a semiconductor circuit as an item for testing the electronic device. For example, jitter of such signal-under-test is measured by a time interval analyzer, an oscilloscope or the like by inputting the signal-under-test thereto. The time interval analyzer or the like allows such jitter to be calculated by measuring phase errors of edges in the signal-under-test for example.
Still more, there has been known a functional test for judging whether or not a pattern of a signal-under-test outputted out of an electronic device coincides with a pattern of an expected values as an item for testing the electronic device. In this test, a testing apparatus detects a data pattern of the signal-under-test by comparing a voltage values of the signal-under-test outputted out of the electronic device with threshold voltage when a predetermined test pattern is inputted to the electronic device. Then, it judges whether or not the data pattern coincides with the pattern of the expected values.
It has been thus necessary to prepare the apparatus for measuring jitter and the apparatus for testing functionality of the device in order to carry out the jitter test in addition to functional tests as described above. Therefore, it has been costly to carry out the jitter test.
Still more, the apparatus of functional test compares the voltage value of the signal-under-test with the threshold voltage at preset timing. Therefore, it can detect the edge position or timing, over which the data pattern of the signal-under-test transits bit by bit, by shifting the comparison timing. It is then conceivable to be able to measure jitter by utilizing this function, i.e., by using the apparatus for performing functional testing.
However, the conventional apparatus for functional testing sets and uses sampling timings based on a test rate synchronized with the operating period of the signal-under-test. Therefore, for each test rate it is necessary to set phase of the sampling timing in order to gradually shift the relative phase of the sampling timing with respect to the signal-under-test within each test rate. It has been thus necessary to carry out the cumbersome timing setting in order to carry out the jitter test, and it has taken a significantly long time for testing. Still more, its measuring accuracy is insufficient and is not suitable for tests because its timing is shifted in the relative phase fashion.
When jitter is measured by using an oscilloscope or the like, the signal-under-test to be inputted therein contains amplitude noise components in addition to the timing noise component. Therefore, it has been difficult to accurately measure only the timing noise of the signal-under-test.
Accordingly, it is an advantage of the invention to provide a measuring apparatus, a measuring method, a testing apparatus, a testing method and an electronic device, which are capable of solving the above-mentioned problem. This advantage may be achieved through the combination of features described in independent claims of the invention. Dependent claims thereof specify preferable embodiments of the invention.